Improve dialect handling

src/main/java/ca/uhn/fhir/jpa/starter/util/JpaHibernatePropertiesProvider.java

@@ -2,31 +2,44 @@ package ca.uhn.fhir.jpa.starter.util;
 
 import ca.uhn.fhir.context.ConfigurationException;
 import ca.uhn.fhir.jpa.config.HibernatePropertiesProvider;
+import ca.uhn.fhir.util.ReflectionUtil;
 import org.hibernate.dialect.Dialect;
 import org.hibernate.engine.jdbc.dialect.internal.StandardDialectResolver;
 import org.hibernate.engine.jdbc.dialect.spi.DatabaseMetaDataDialectResolutionInfoAdapter;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 import org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean;
 
 import java.sql.Connection;
 import java.sql.SQLException;
 import javax.sql.DataSource;
 
+import static org.apache.commons.lang3.StringUtils.isNotBlank;
+
 public class JpaHibernatePropertiesProvider extends HibernatePropertiesProvider {
+	private static final Logger ourLog = LoggerFactory.getLogger(JpaHibernatePropertiesProvider.class);
 
-	private final Dialect dialect;
+	private final Dialect myDialect;
 
-	public JpaHibernatePropertiesProvider(LocalContainerEntityManagerFactoryBean myEntityManagerFactory) {
-		DataSource connection = myEntityManagerFactory.getDataSource();
-		try (Connection dbConnection = connection.getConnection()) {
-			dialect = new StandardDialectResolver()
+	public JpaHibernatePropertiesProvider(LocalContainerEntityManagerFactoryBean theEntityManagerFactory) {
+		String dialectClass =
+			(String) theEntityManagerFactory.getJpaPropertyMap().get("hibernate.dialect");
+		if (isNotBlank(dialectClass)) {
+			myDialect = ReflectionUtil.newInstanceOrReturnNull(dialectClass, Dialect.class);
+		} else {
+			ourLog.warn("'hibernate.dialect' not set in application configuration! Please explicitly specify a valid HAPI FHIR hibernate dialect.");
+			DataSource connection = theEntityManagerFactory.getDataSource();
+			try (Connection dbConnection = connection.getConnection()) {
+				myDialect = new StandardDialectResolver()
 					.resolveDialect(new DatabaseMetaDataDialectResolutionInfoAdapter(dbConnection.getMetaData()));
-		} catch (SQLException sqlException) {
-			throw new ConfigurationException(sqlException.getMessage(), sqlException);
+			} catch (SQLException sqlException) {
+				throw new ConfigurationException(sqlException.getMessage(), sqlException);
+			}
 		}
 	}
 
 	@Override
 	public Dialect getDialect() {
-		return dialect;
+		return myDialect;
 	}
 }